Page 48 - Data Structures Interactive Book

the stack is empty when the top pointer is NULL. These checks prevent invalid operations and

ensure program stability.

5.4 Applications in Computer Science

Stacks are widely used in computer science because of their simple yet powerful

behavior. They appear in many algorithms and system-level processes.

5.4.1 Expression Evaluation (Postfix, Prefix, Infix)

Stacks are essential for evaluating and converting mathematical expressions. For

example, converting an infix expression (like A + B * C) into postfix (A B C * +) requires a stack

to temporarily hold operators. During evaluation, operands are pushed onto the stack, and

operators are applied in the correct order, ensuring accurate results.

5.4.2 Balanced Parentheses Checking

Stacks are used to verify whether parentheses, brackets, or braces in an expression

are properly balanced. Each opening symbol is pushed onto the stack, and each closing symbol

checks the top of the stack. If the symbols match, the stack is popped; otherwise, the
expression is invalid. This principle is widely used in compilers and interpreters.

5.4.3 Function Call Management (Recursion)

Recursion relies heavily on stacks. Each function call is pushed onto the call stack with

its local variables and return address. When the function completes, it is popped from the
stack, and control returns to the previous function. This mechanism allows recursive

algorithms to work correctly, such as computing factorials or traversing trees.

5.5 Limitations of Stacks

Despite their usefulness, stacks have limitations. Array-based stacks suffer from fixed

size, which can lead to overflow if too many elements are pushed. Linked list-based stacks

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